Fan comprising an electronically commutated drive motor

ABSTRACT

A fan having an electronically commutated drive motor ( 27 ) has a bearing tube ( 62 ) having an inner side and an outer side. The internal stator of the drive motor ( 27 ) is arranged in the region of the outer side. An external rotor ( 28 ) of said motor interacts during operation with the internal stator ( 72 ). Fan blades ( 26 ) of the fan ( 22 ) are arranged on the outer periphery of the external rotor ( 28 ). Bearing elements ( 52, 54 ), by means of which a shaft ( 46 ) connected to the external rotor ( 28 ) is journaled, are arranged on the inner side of the bearing tube ( 62 ). Conduits ( 90 ), which enable coolant to flow through the bearing tube ( 62 ) during operation of the fan ( 22 ), are provided in the bearing tube ( 62 ).

FIELD OF THE INVENTION

The invention relates to a fan having an electronically commutated drivemotor.

BACKGROUND

Such fans are used principally as so-called “equipment fans” for coolingelectronic devices, for example for cooling computers, servers, circuitboards, etc. Such fans must be extremely inexpensive, but, on the otherhand, are expected to be highly reliable and to have a service life atleast as long as the service life of the device cooled by the fan.

Such fans contain a variety of elements, for example Hall sensors, ICs,transistors, capacitors, etc., as well as bearings, for example plainbearings, rolling bearings, etc.

That element which is most greatly jeopardized by high operatingtemperatures is referred to as the “performance-determining element.”Depending on the construction of the fan, this can therefore be anelectronic or a mechanical element.

Higher temperatures occur in particular in fans having a plastichousing, since the heat created during operation can be dissipated onlyvery poorly by the plastic, so that hot regions, which can also bereferred to as “hot spots,” can be produced in the interior of such afan.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to make a novelheat-dissipating fan structure available.

This object is achieved, according to the invention, by a fan having aninternal stator, an external rotor coupled to a central shaft, rotatablyjournaled inside a bearing tube containing a plurality of bearings,wherein, to facilitate cooling and avoid “hot spots,” the cylindricalwall of bearing tube is formed with a plurality of conduits throughwhich a coolant, for example air, can pass, thereby dissipating heat.Preferably, the conduits are longitudinal and mutually parallel.

Coolant (i.e. generally air) can flow through the conduits, provided inthe wall of the bearing tube between the internal stator and the bearingelements, so that the waste heat created in the lamination stack cannotbe transferred directly to the bearing elements in the bearing tube.This is the case, in particular, for the bearing element adjacent therotor shaft base, the temperature of which bearing element is lowered bythe coolant, so that the temperature at this sensitive location can bereduced, thereby correspondingly extending the service life of thebearing element there, and thus the service life of the fan as a whole.

With an appropriate design, a bearing tube of this kind can beimplemented to be very light and very economical of material, but stillsufficiently rigid and functionally suitable, for example in terms ofcooling at critical locations.

BRIEF FIGURE DESCRIPTION

Further details and advantageous refinements of the invention areevident from the exemplifying embodiment, in no way to be understood asa limitation of the invention, that is described below and depicted inthe drawings.

FIG. 1 is a perspective depiction of the housing of an axial fan priorto installation of the drive motor and the fan wheel, the bearing tubebeing visible at the center;

FIG. 2 is a depiction analogous to FIG. 1, from a slightly differentangle of view and at greatly enlarged scale;

FIG. 3 is a depiction viewed from the underside of the depiction of FIG.2, i.e. in the direction of arrow III of FIG. 1;

FIG. 4 depicts a rotor on which a fan wheel is arranged;

FIG. 5 is a perspective depiction of housing, drive motor, and fanwheel, viewed approximately in the direction of arrow III of FIG. 1;

FIG. 6 is a perspective depiction of housing, drive motor, and fanwheel, viewed from a perspective similar to that of FIG. 1;

FIG. 7 is a longitudinal section through the assembled fan, similar tothe depiction of FIG. 5;

FIG. 8 depicts measurement curves; this figure shows the measurementsfor a fan not having conduits in the bearing tube and for use of astandard rotor not having a radial fan wheel;

FIG. 9 is a depiction analogous to FIG. 8 for a fan of the same size asin FIG. 8 but having a radial fan wheel in the rotor and having conduitsin the bearing tube, although here they are closed off so that aircannot flow through them; and

FIG. 10 is a depiction analogous to FIGS. 8 and 9 for a fan of the samesize as in those figures, but having a radial fan wheel in the rotor andhaving conduits in the wall of the bearing tube which are open, so thatair can flow through them during operation, as indicated schematicallyin FIG. 7.

DETAILED DESCRIPTION

FIG. 1 shows housing 20 of a typical equipment fan 22 that is depictedin the assembled state in FIG. 6. Fan 22 here has a fan wheel 24 havingseven fan blades 26, which are mounted on the central rotor 28 of adrive motor 27 and, in FIG. 6, rotate in the direction of an arrow 30,i.e. counter-clockwise, so that in FIG. 6 air is transported through fan22 in the direction of an arrow 34, i.e. from top to bottom. The resultis to produce a corresponding pressure difference at fan 22, i.e. inFIG. 6 the pressure is greater at the bottom than at the top.Flow-through direction 34 of the transported air is also schematicallydepicted in FIG. 7 for the right half of that Figure.

Fan wheel 24 is depicted in FIG. 4 from the lower (in FIG. 6) side.Rotor 28 has on its outer side a pot- or bell-shaped housing 29 that ismade of plastic and is integral with blades 26, as clearly shown in FIG.5.

A magnetic yoke 40, whose shape is best gathered from FIG. 7, is mountedin housing 29 by molding. The upper (in FIG. 4) end 44 of a rotor shaft46 is cast, by means of a suitable metal alloy 42 (e.g. ZAMAK) in acollar 41 in the center of yoke 40. Also preferably produced in thecasting operation is a small radial fan wheel 48 that keeps air movingthere during operation and that improves cooling, particularly in theregion of the winding ends. In some cases, such a fan wheel is notnecessary, this being ascertained by experiment. Upper end 44 of shaft46 has an annular groove 45 into which metal alloy 42 engages (see FIG.7). A multi-pole, radially magnetized ring magnet 47 is mounted in yoke40.

Shaft 46 is journaled in two bearings 52, 54, in this case in ballbearings, whose inner rings are slid onto shaft 46. The inner ring ofthe lower (in FIG. 7) bearing 54 is additionally retained by a snap ring56.

The outer ring of upper bearing 52 is pressed from above into an opening60 of a bearing tube 62 as far as a stop 64, and the outer ring of lowerbearing 54 is likewise pressed from below into an opening 66 of bearingtube 62 to the same stop 64. The latter holds the two outer rings at apredefined spacing.

Bearing tube 62 has a wall 59, whose inner surface is designated 61 andwhose outer surface is designated 63. It is manufactured from a suitableplastic that has the requisite mechanical stability and heat resistance.It is, in this case, integral with a flange 70 whose function is tosupport internal stator 72 of drive motor 27 and the associated circuitboard 76 for the motor electronics. This flange 70 is held by spokes 78in outer ring 80 of housing 20.

Internal stator 72 has a lamination stack 84 equipped with a statorwinding 82 (see FIG. 7), which stack is pressed onto ribs 81 on theouter side 63 of bearing tube 62 as far as a stop 86 (FIG. 2) so thatwaste heat from lamination stack 84 is transferred to wall 59 of bearingtube 62 and, via the latter, in particular to upper bearing 52 (FIG. 7).

Wall 59 of bearing tube 62 is equipped with, for example, ten continuousconduits 90 (FIG. 2) whose angular extent alpha can be equal to, forexample 25°. Extending between them are radial ribs 92 having an angularextent of, for example, 11°, i.e. the angular extent of conduits 90 isapproximately 1.5 to three times the angular extent of ribs 92. Ribs 81are located radially outside conduits 90.

As FIGS. 3 and 5 show, conduits 90 extend through flange 70 so thatcooling air can flow, in FIG. 7, from the discharge (lower) side of fan22 upward through conduits 90, as indicated by arrows 94 schematicallyand only for the right side of FIG. 7. This air 94 cools wall 59 ofbearing tube 62 and transports, upward in FIG. 7, the heat that travelsfrom lamination stack 84 into bearing tube 62.

This air flows there, along arrows 96, over the winding ends of statorwinding 82, downward between the stator poles, and then from there alongarrows 98 to a gap 100 between rotor 28 and flange 70; there it isentrained (Venturi effect) by the air flowing past in the direction ofarrows 34, so that a continuous and powerful air circulation takes placein internal stator 72 during operation, cooling principally the upperbearing 52 and stator winding 82 and thereby lengthening the servicelife of fan 22 (see FIG. 10).

Bearing tube 62 thus has a honeycomb structure in cross section, makingit possible to lengthen the service life of the fan without additionaloutlay. Radial fan wheel 48 (if present) causes a distribution of thecirculating air in the upper (in FIG. 7) part of internal stator 72, andthereby produces uniform cooling.

FIG. 8 shows measurement curves for a standard fan in which a radial fanwheel is not provided in rotor 28, and in which a solid bearing tube,not having a honeycomb structure, is used.

The symbol P designates the electrical power level, plotted on theright-hand scale in FIG. 8.

The measured room temperature is labeled 102, and in this case is equalto 24° C.

Curve 104 is the temperature difference of stator winding 82 (FIG. 7)relative to room temperature 102, i.e. for a volumetric flow rate ofzero, this temperature difference is equal to 38° K, and at 380 m³/h, itdecreases to 22° K.

Curve 106 is the temperature difference of upper ball bearing 52, and108 is the temperature of lower ball bearing 54, both relative to roomtemperature. It is evident that the upper (in FIG. 7) ball bearing 52 ishotter than lower ball bearing 54 because the upper ball bearing isbeing cooled less effectively.

FIG. 9 shows measurement curves for a bearing tube 62 that has ahoneycomb structure, but in which conduits 90 are closed off.

Once again, P designates the electrical power level, the curve for whichis similar to that in FIG. 8 and is likewise plotted on the right-handscale in FIG. 9.

Room temperature is labeled 112 and in this case is equal to 23° C.

Curve 114 is the temperature difference of stator winding 82 withrespect to room temperature.

Curve 116 is the temperature difference of upper ball bearing 52 withrespect to room temperature. Curve 118 shows the temperature differenceof lower ball bearing 54 with respect to room temperature. It is evidentthat upper ball bearing 52 is approximately 5° K hotter than lower ballbearing 54.

FIG. 10 shows measurement curves for a bearing tube 62 having ahoneycomb structure as depicted in FIG. 2, conduits 90 being open, sothat air flows through conduits 90 and through motor 27 as indicatedschematically in FIG. 7 by flow arrows 94, 96, 98. Radial fan wheel 48(FIG. 4) is also provided. Once again, P designates the electrical powerlevel.

A comparison of FIGS. 9 and 10 shows the considerable difference.

Room temperature is labeled 122 in FIG. 10, and is equal here to 23° C.

The difference between the winding temperature and room temperature islabeled 124, and is somewhat lower than in FIG. 9 because winding 82 isbeing cooled better.

The temperature difference between upper ball bearing 52 and roomtemperature is labeled 126, and is 10° K lower here than in FIG. 9, i.e.upper ball bearing 52 is being cooled substantially better in FIG. 10than in FIG. 9.

The temperature difference between lower ball bearing 54 and roomtemperature 122 is labeled 128. That difference is approximately 7° Kless than in FIG. 9, i.e. bearing 54 is also being cooled substantiallybetter, so that what results as a whole, from the measures and featuresaccording to FIGS. 1 to 7, is a substantially longer service life forfan 22, without the need for additional costs for that purpose.

Numerous variants and modifications are, of course, possible within thescope of the invention.

1. A fan comprising an electronically commutated drive motor (27) havingan internal stator (72) and an external rotor (28) cooperatingtherewith, said external rotor being supported by a central shaft (46)connected therewith; a plurality of fan blades (26) being arranged on anouter periphery of said external rotor (28); and a bearing tube (62)having an outer side (63) and an inner side (61), a plurality ofbearings (52,54) being arranged on said inner side (61), journaling saidcentral shaft (46) for rotation therein; wherein the bearing tube (62)includes, between said outer side (63) and said inner side (61), a wallformed with cooling conduits (90), enabling streaming of coolant throughthe wall, said inner side (60, 66) of said bearing tube separating saidcooling conduits (90) from said bearings (52, 54) arranged within saidbearing tube (62).
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 13. The fan according to claim1, wherein the bearing tube (62) is formed, at least in part, of plasticmaterial.
 14. The fan according to claim 1, wherein said coolingconduits (90) in said bearing tube wall (59) are arranged in a patternwhose cross-section resembles a honeycomb.
 15. The fan according toclaim 1, wherein said bearing tube (62) is arranged on a flange (70)oriented generally perpendicular to an axis of said bearing tube, and atleast some of said cooling conduits (90) extend axially through saidflange (70).
 16. The fan according to claim 1, wherein, in said wall(59) of said bearing tube (62), a plurality of carrier segments or ribs(92) are provided, each extending radially from said inner side (61) tosaid outer side (63).
 17. The fan according to claim 16, wherein,measured in a circumferential direction, an average angular extent ofsaid cooling conduits (90) exceeds an average angular extent of saidcarrier segments (92) by a factor of 1.5 to
 3. 18. The fan according toclaim 1, wherein bearing seats (64) for said bearings (52, 54) areformed on said inner side (61) of said bearing tube (62).
 19. The fanaccording to claim 1, wherein said fan, when operating, creates apressure differential between a first longitudinal end of said coolingconduits (90) and a second longitudinal end thereof, thereby causingcooling air to stream (94) through said cooling conduits (90).
 20. Thefan according to claim 1, wherein said external rotor (28) has a bellconfiguration, with an internal center, to which said central shaft (46)is attached.
 21. The fan according to claim 20, wherein the shaft (46)is cast into a recess formed on the inside of the rotor bell.
 22. Thefan according to claim 21, wherein a radial fan wheel (48) isimplemented from the material with which the shaft (46) is cast into therecess at the base of the bell, which fan wheel has the function ofdistributing, in the region of the base of the bell, coolant flowing outof the conduits (90) provided in the bearing tube (62).
 23. The fanaccording to claim 20, wherein, to facilitate the discharge of coolantfrom the fan (22), a gap (100) is provided, past which air moved (34) bysaid fan blades (26) passes, thereby creating an underpressure adjacentthis gap (100).
 24. The fan according to claim 23, wherein said gap(100) is defined by a spacing between said flange (70) and acircumferential rim of said bell-shaped rotor (28), and passage of airfrom said fan blades (34) causes a Venturi effect, entraining coolantexiting (98) via said gap (100).